Toothed belt

ABSTRACT

Described herein is a toothed belt comprising: a body made of elastomeric material having teeth on one of its surfaces; a coating fabric adherent to the surface of the teeth; and resistant inserts capable of having a high power of transmission, obtained by means of appropriate selection of parameters. The toothed belt according to the invention comprises a body formed by a mixture with a hardness value, after vulcanization, of between 90 and 97 shoreA, preferably made of chloroprene: the fabric is formed by at least one layer of fibres with a weight of between 700 and 1250 grams per square metre of surface, and preferably is a 6/6 textured polyamide, and the resistant inserts are made of glass fibres with a mean diameter of between 2.4 and 3 mm and are formed starting from basic filaments having a mean diameter of between 6 and 10 μm, which are preferably formed for at least 75 wt % of basic filaments having a mean diameter of 9 μm.

[0001] The present invention relates to a high-performance toothed belt.

BACKGROUND OF THE INVENTION

[0002] Toothed belts comprise a body made of elastomeric material havingteeth on one of their surfaces, a coating fabric adherent to the surfaceof the teeth and resistant inserts, hereinafter also referred to ascords, inside the body.

[0003] Each component of the belt contributes to increasing theperformance thereof in terms of strength, so as to reduce the risk ofbreaking of the belt and increase the specific power of transmission.

[0004] The coating fabric of toothed belts protects the working surfaceof the belt from wear due to rubbing between the sides of the teeth ofthe belt and the sides of the slots of the pulley with which the beltinteracts and meshes. In addition, the coating fabric prevents thesubstances present in the environment in which the toothed belt worksfrom possibly damaging it, and reduces the deformability of the teethand the coefficient of friction on the working surface, i.e., the areaof contact between belt and pulley during meshing.

[0005] Known is the use of a coating fabric consisting of a singlelayer, for example, having a weight of between 100 and 500 grams persquare metre of surface of fabric, in order to ensure the necessaryresistance to abrasion, maintaining an adequate flexibility of the beltwhen it is winding onto the pulley. Alternatively, also known is the useof a coating made up of a double layer of fabric for improving thecharacteristics of belt strength and for increasing the operating lifeof the toothed belt.

[0006] The resistant inserts of high performance belts in terms of powerof transmission, i.e., for belts that have a specific power oftransmission of higher than 25 kW per cm of width, are currently madewith steel cords or aramidic-fibre cords, for example, the onesavailable on the market with the trademarks Kevlar® or Twaron®.

[0007] Aramidic fibres, as has been known for some time now, present,however, the disadvantage of having a dimensional stability over timethat is very low; consequently, a belt of resistant inserts made ofaramidic fibres, during storage, undergoes a shortening of its freedevelopment, with consequent alteration (i.e., reduction) of the initialpitch. As a result, during use, the belt is subjected to a higher loadand higher stresses, which normally determine an early deterioration,triggered by the meshing error that is generated between the belt andthe pulley. Furthermore, resistant inserts made of aramidic fibresrequire a particularly complex and costly adherization treatment forimproving the dimensional stability over time of the resistant insertitself, and moreover, if this treatment is not carried out carefully, italso entails problems during cutting of the belts.

[0008] On the other hand, resistant inserts made of steel have a highdimensional stability over time but have a high specific weight and,furthermore, since the depositing of the reinforcement element takesplace according to a helical pattern, during cutting of the belts theseresistant elements partially come out of the side edges of the belt,with the risk of causing injury to operators during installation of thebelt.

[0009] In order to prevent the above risk, it is therefore necessary toproceed to a further finishing step, which envisages removal of thestrands of cords that protrude as a result of cutting and envisagesmanual sealing of all the edges of the belt using adhesive in the areaswhere the filaments partially protrude. This further finishing stepinvolves considerable additional costs, in so far as it has to becarried out manually and has to be performed on each individual belt.

[0010] Furthermore, for high powers of transmission, on account of theproblems of rapid wear of known rubber belts, there are still usedsystems of mechanical transmission employing chains or gears, which,however, present disadvantages in terms of weight, noise, maintenancecosts and costs due to their complexity owing to the need forlubrication, whilst it would be advantageous to be able to use a rubberbelt also for such applications.

SUMMARY OF THE INVENTION

[0011] The purpose of the present invention is therefore to provide atoothed belt that does not present the drawbacks described above and, inparticular, a toothed belt having a high specific power of transmission,so as to be able to replace the mechanical drive systems currently inuse.

[0012] It has surprisingly been found that a belt obtained byappropriately selecting certain constructional parameters enables allthe drawbacks referred to above to be solved, as well as to have, at thesame time, a high power of transmission.

[0013] According to the present invention, there is thus provided atoothed belt comprising a body made of elastomeric material having teethon one of its surfaces, a coating fabric adherent to the surface of theteeth, and resistant inserts, the said belt being characterized in that:

[0014] said body comprises a main elastomer with a hardness value, aftervulcanization, of between 90 and 97 shoreA and comprises at least onepolymer chosen in the group consisting of acrylonitrile/butadiene,acrylonitrile, hydrogenated butadiene, chlorosulphonated polyethylene,chloroprene and polyurethane;

[0015] said fabric is formed by at least one layer of fibres and has atotal weight of between 700 and 1250 g per square metre of surface;

[0016] said resistant inserts are made of glass fibres with a meandiameter of between 2.4 and 3 mm, are formed starting from basicfilaments or strands having a mean diameter of between 6 and 10 μm, sothat said belt altogether has a tensile strength of between 75 000 and90 000 N over a basic width of the belt of 30 mm and by linearextrapolation hence between 25 000 and 30 000 N per cm of belt width.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a better understanding of the present invention, it will nowbe further described also with reference to the attached figures, inwhich:

[0018]FIG. 1 is a partial perspective view of a toothed belt accordingto the present invention; and

[0019]FIG. 2 is a creep test conducted on the toothed belt according tothe invention and on a comparison belt.

DETAILED DESCRIPTION OF THE INVENTION

[0020] With reference to FIG. 1, the number 1 designates, as a whole, atoothed drive belt. The belt 1 comprises a body 2 made of elastomericmaterial, in which a plurality of longitudinal filiform resistantinserts 3 are embedded.

[0021] The body 2 has a toothing 4 which is coated with a coating fabric5, which has weft threads 6 that extend in the longitudinal direction ofthe belt 1 and warp threads 7 oriented in the transverse direction ofthe belt 1.

[0022] The body 2 comprises a mixture of elastomeric material having ahardness, after vulcanization, of between 90 and 97 shoreA, measuredaccording to the standard procedure envisaged by the ASTM standard 2240,with a measuring time of one second, obtained without recourse to theaddition of reinforcement fibres.

[0023] The mixture of elastomeric material comprises a main elastomer,preferably chosen in the group made up of acrylonitrile/butadiene,acrylonitrile/hydrogenated butadiene, chlorosulphonated polyethylene,ethylene-propylene-diene terpolymer (EPDM), and chloroprene.

[0024] Even more preferable is a mixture having a chloroprene orpolyurethane base, i.e., a mixture containing more than 80% ofchloroprene or polyurethane, where by polyurethane is meant abicomponent mixture by injection or a thermoplastic by extrusion.

[0025] The mixture of elastomeric material may contain, in addition tothe main elastomer, conventional additives such as reinforcement agents,fillers, pigments, stearic acid, accelerators, vulcanization agents,antioxidants, activators, initiators, plasticizing agents, wax,pre-vulcanization inhibitors, and the like. For instance, as filler awhite filler or carbon black may be used, this generally being added inan amount of between 5 and 200 phr, preferably, approximately 70 phr.There may also be added talc, calcium carbonate, silica and the like inamounts of generally between 5 and 150 phr or dispersions in oilcontaining fillers. It is possible to use organosilanes in amounts ofbetween 0.1 and 20 phr. It is possible to use sulphur-donorvulcanization agents, for example aminodisulphides and polymericpolysulphides, or free sulphur. The amount added varies according to thetype of rubber and the type of vulcanization agent used, and isgenerally between 0.1 and 10 phr. Amongst the antidegrading agents mostwidely used in the composition of the mix there are microcrystallinewaxes, paraffin waxes, monophenols, bisphenols. thiophenols,polyphenols, derivatives of hydroquinone, phosphites, mixtures ofphosphates, thioesters, naphthyl amines, diphenol amines, derivatives ofsubstituted and non-substituted diaryl amines, diarylphenylene diamines,paraphenylene diamines, quinolines, and mixtures of amines. Theantidegrading agents are generally used in amounts of between 0.1 and 10phr. Representatives of process oils that can be used aredithiobisbenzanilide, polyparadinitrosobenzene, xilyl mercaptans,polyethylene glycol, petroleum oils, vulcanized vegetable oils, phenolicresins, synthetic oils, petroleum resins, and polymeric esters. Theprocess oils can be used in conventional quantities between 0 and 70phr. Amongst the initiators, stearic acid is conventionally used inamounts of between 1 and 4 phr. Conventional additives may also beadded, such as calcium oxide, zinc oxide and magnesium oxide, generallyin amounts of between 0.1 and 15 phr. Conventional accelerators are alsoused, or combinations of accelerators such as amines, disulphides,guanidine, thiourea, thiasols, thiols, sulphenamides, dithiocarbamates,and xanthates, generally in amounts of between 0.1 and 15 phr.Reinforcement compounds may also be added in amounts preferably ofbetween 10 and 20 phr.

[0026] The coating fabric 5 of the toothed belt 1 may consist of one ormore layers, and has a total weight, made up of the weight of the sum ofthe layers that form the raw fabric, plus that of the treatments towhich the raw fabric has been subjected, of between 700 and 1250 g persquare metre of surface. The total weight is even more preferablybetween 700 and 1100 g/m², when it is made up of a single layer, andbetween 850 and 1250 g/m², when it is made up of a double layer.

[0027] In the case where it is formed by a single layer it may, forexample, be obtained using the weaving technique known as 2×2 twill, andhas a total thickness of between 230 and 280 mm and consists of a weftcomprising first threads and second threads interwoven together. Thefirst threads have a count of 4×110 and are made up of a number ofprimary strands of 4×34, and the second threads have a count of 6×78 andare made up of a number of primary strands of 6×34.

[0028] The first and second threads consist of a polymeric material,preferably aliphatic or aromatic polyamide and, even more preferably,6/6 polyamide and, in detail, the first threads are made ofmedium-toughness 6/6 polyamide and the second threads are made ofhigh-toughness 6/6 polyamide, for a greater resistance to wear.

[0029] The fabric 5 may moreover consist of two layers and, in thiscase, has a total thickness of between 1.8 and 2.3 mm. The two combinedlayers of fabric are each made, both as regards the weft and as regardsthe warp, with threads made of a polymeric material, preferablyaliphatic or aromatic polyamide, even more preferably, 6/6 polyamideand, in particular, high-toughness 6/6 polyamide.

[0030] The coating fabric 5 is, in any case, chosen in such a way as tohave a tensile strength in the non-elastic direction (warp) of between3000 and 5500 N over 25 mm of width, and an extensibility in the elasticdirection (weft) of between 130 and 180%. The coating fabric 5 isgenerally treated with an adhesive, in particular rorcinol-formaldehydelatex (RFL), preferably in an amount of between 25 and 35 wt %, in orderto improve adhesion of the fabric 5 to the body 2 and resistance toabrasion of the belt 1 as a whole.

[0031] After treatment with RFL, the fabrics are subjected, in aconventional way, to successive steps of spreading with mixes preferablyof the same type as described previously for the body of the belt. Thefabric 5 acquires a high degree of antistaticness, which is sufficientand necessary for meeting the requirements contemplated by the referencestandard for toothed belts, namely the standard BSI2050, a 50% modulus,i.e., the tensile force necessary for lengthening the original dimensionof the specimen of fabric by 50%, of between 70 and 200 N over 50 mm ofwidth. The resistant inserts 3 are made of high-modulus glass fibres,starting from basic filaments having a mean diameter of between 6 and 10μm, for example, the ones available on the market under the name of KGlass or U Glass, manufactured by NGF, or S-Glass, manufactured andmarketed by Asahi.

[0032] Preferably, basic filaments having a mean diameter of 9 μm areused, in an amount greater than 75% of the total weight of the resistantinserts 3 themselves. The above basic filaments undergo a treatmentbased upon an adhesive composition, for example RFL, which brings thediameter of the filament to a size preferably between 0.006 and 0.012mm. Consequently, a number of between 150 and 250 of these basicfilaments or strands are joined together to obtain a single thread andthen in groups of nine twisted together in a first direction, so as toobtain a first basic twisted yarn. Finally, seventeen of these basictwisted yarns are then twisted in a second direction opposite to thefirst direction to obtain the resistant insert or cord.

[0033] The resistant insert or cord has a total diameter of between 2.4and 3 mm and a number of twists of approximately 40±6 per linear metreof cord and a weight of between 600 and 700 grams per hundred metres.

[0034] The resistant insert thus obtained is then deposited on the mouldfor construction of the belt with a spiralling pitch of between 2.7 and3.2 mm, so obtaining a number of turns of between 7 and 11 for every 3cm of width of the toothed belt itself. In this way, it emerges that thetensile strength of the belt is between 25 000 and 30 000 N per cm ofwidth, with an extensibility of less than 4.5%.

[0035] Surprisingly, it has been found that, by selecting thecombination of resistant inserts 3, coating fabric 5 and elastomericmaterial constituting the body, as described previously, a belt capableof having on the pulleys a high power of transmission is obtained, inparticular when the pitch of the belt is between 12 and 17 mm.

[0036] In particular, in the case where the pitch of the belt is 14 mm,with a width of 40 mm and the pulley being used has 80 teeth, themaximum power of transmission at 1700 r.p.m. is 257 kW (64 kW per cm ofwidth), with an increase of 50% as compared to toothed belts currentlyin use.

[0037] The belt according to the present invention can be made usingcommon methods for manufacturing toothed belts.

[0038] From an examination of the characteristics of the toothed beltmade according to the present invention, the advantages that it affordsare evident. In particular, thanks to the high power of transmission,the belt may be used also for replacing mechanical systems currently inuse. In addition, thanks to the particular combination of the parametersof construction, it is possible to avoid the drawbacks connected to theuse of cords made of aramidic fibres and steel fibres and, inparticular, the addition of further very costly finishing steps, in thisway simplifying also the cutting process.

[0039] The toothed belt according to the present invention will now bedescribed also with reference to examples, without thereby limiting thescope of the invention to the said examples.

EXAMPLE 1

[0040] Table 1 gives the composition of the mix constituting the body 2of a toothed belt A according to the invention. The said belt is foundto have a hardness, measured after vulcanization, of 93-94 shoreA,whilst the comparison belt B has a hardness of 88-90 shoreA. TABLE 1Composition A Composition B Amount (phr) Amount (phr) Chloroprene 100100 White 70 56 filler/carbon black Diphenylamine 6 6 oxylate Zinc oxide7 8.5 Stearic acid 9.5 4.6 Resorcinol 8 8 Reinforcing up to 20 up to 8components

EXAMPLE 2

[0041] Table 2 gives the characteristics of the weft and warp of acoating fabric 5 of a toothed belt 1 according to the present invention.TABLE 2 Characteristics of the weft Construction of the weft Doublelayer of threads of weft of textured 6/6 polyamide First layer of weftmedium-toughness 6/6 polyamide Count (dtex) 4 × 110 Number of strands 4× 34  Second layer of weft high-toughness polyamide Count (dtex) 6 × 78 Number of strands 6 × 34  Picks (number/25 mm) 98 ± 3  Tensile strength(N/25 mm) >1500 Extensibility (%) 170 ± 10  Elongation at 100 N (%) 90 ±10 Characteristics of the warp Construction of the warp Single layer ofhigh- toughness 6/6 polyamide Count (dtex) 940 Number of strands 140Ends (number/25 mm) 105 ± 3  Tensile strength (N/25 mm) >5000Extensibility (%) >25 

EXAMPLE 3

[0042] Table 3 gives the characteristics of resistant inserts or cords(3) used for the manufacture of a toothed belt A 5 according to theinvention and of comparison belts B and C made, respectively, withresistant inserts made of glass fibres of a conventional type and onesmade of aramide. TABLE 3 A B C Number of 180-220 720-880 720-880 basicstrands Diameter of 9 9 12   individual strand First twisting 2 2 2.5(twists/25 mm) Final twisting   1 ± 0.2   1 ± 0.3 1.1 in oppositedirection (T/25 mm) Primary 2 2  2.27 twist/final twist ratio Finaldiameter 2.65 ± 0.15 2.47 ± 0.15 2.66 ± 0.10 of cord (mm) Final tensile525 ± 25  300 ± 50  630 ± 30  strength of cord (daN) Extensibility 4.5 ±0.5 3.5 ± 1.0 3.5 ± 0.5 (%) Elongation at max 1.8 max 1.8 max 1.0 100daN (%) Weight 690 ± 10  630 ± 30  480 ± 20  (g/100 m)

EXAMPLE 4

[0043] Table 4 gives the values obtained from a number of testsconducted on a belt made according to the present invention. TABLE 4Values found with standard tests Tensile strength (N) 81700Extensibility (%) 4.5 Mix/cord adhesion (N/cm) 200 Pdl (mm) two fabrics1.42 Pdl (mm) one fabric 1.37 Creep test (% creep after −9% max 12 h)

[0044] The width of the belt tested was 30 mm.

EXAMPLE 5

[0045] The graph appearing in FIG. 2 shows the values obtained from acreep test using a belt according to the present invention (curve A) anda comparison belt (curve B), the latter, however, comprising a mixaccording to what is given in Table 1 (belt B) and having resistantinserts or cords made of aramidic fibres.

[0046] The test was carried out on a 50 000-N torque meter, with twotoothed pulleys with 24 teeth, on which was mounted a belt with a pitchof 14 mm and a width of 15 mm, an axial load of 14 000 N being appliedto the belt. Then, the distance between centres was blocked and thecreep data (in %) were recorded continuously for 12 hours. The graphgives the values obtained at 16-minute intervals.

1. A toothed belt (1) comprising: a body (2) made of elastomericmaterial having teeth (4) on one of its surfaces; a coating fabric (5)adherent to the surface of the teeth; and resistant inserts or cords(3); said toothed belt (1) being characterized in that: said body (2)comprises a main elastomer with a hardness value, after vulcanization,of between 90 and 97 shoreA, and comprises at least one polymer chosenin the group consisting of acrylonitrile/butadiene, acrylonitrile,hydrogenated butadiene, chlorosulphonated polyethylene, chloroprene andpolyurethane; said fabric (5) is formed by at least one layer of fibresand has a total weight of between 700 and 1250 grams per square metre ofsurface; said resistant inserts or cords (3) are made of glass fibreswith a mean diameter of between 2.4 and 3 mm, are formed starting frombasic filaments having a mean diameter of between 6 and 10 μm, so thatsaid belt altogether has a tensile strength of between 25 000 and 30 000N per cm of belt width.
 2. The toothed belt according to claim 1,characterized in that each individual resistant insert is set with aspiralling pitch of between 7 and 11 turns for every 30 mm of beltwidth, and in that each individual resistant insert has a tensilestrength of between 4500 and 5500 N.
 3. The toothed belt according toclaim 2, characterized in that said resistant inserts (3) consist, forat least 75 wt %, of basic filaments having a diameter of 9 μm.
 4. Thetoothed belt according to claim 3, characterized in that each saidresistant insert is formed by: joining a number of between 150 and 250basic filaments to form first yarns; twisting 9 first yarns in a firstdirection to form first twisted yarns; twisting 17 first twisted yarnsin a second direction opposite to said first direction.
 5. The toothedbelt according to claim 1, characterized in that said body is made forat least 80% of chloroprene.
 6. The toothed belt according to claim 1,characterized in that said body is made for at least 80% ofpolyurethane.
 7. The toothed belt according to claim 1, characterized inthat said fabric (5) consists of a single layer and has a total weightof between 700 and 1100 g/m² and has a total thickness of between 2.3and 2.8 mm.
 8. The toothed belt according to claim 7, characterized inthat said fabric (5) is woven using the 2×2 twill technique.
 9. Thetoothed belt according to claim 8, characterized in that said fabric (5)comprises textured fibres.
 10. The toothed belt according to claim 9,characterized in that said fabric (5) comprises polyamide fibres. 11.The toothed belt according to claim 10, characterized in that saidfabric (5) comprises 6/6 polyamide fibres.
 12. The toothed beltaccording to claim 11, characterized in that said fabric (5) compriseshigh-toughness 6/6 polyamide fibres and medium-toughness 6/6 polyamidefibres.
 13. The toothed belt according to claim 1, characterized in thatsaid fabric (5) consists of a double layer and has a total weight ofbetween 850 and 1250 g/m² and a total thickness of between 1.8 and 2.3mm.
 14. The toothed belt according to claim 13, characterized in thatsaid fabric (5) comprises textured fibres.
 15. The toothed beltaccording to claim 14, characterized in that said fabric (5) comprisespolyamide fibres.
 16. The toothed belt according to claim 15,characterized in that said fabric (5) comprises 6/6 polyamide fibres.17. The toothed belt according to claim 16, characterized in that saidfabric (5) comprises high-toughness 6/6 polyamide fibres andmedium-toughness 6/6 polyamide fibres.
 18. The toothed belt according toclaim 1, characterized in that it has a pitch of between 12 and 17 mm.19. The toothed belt according to claim 1, characterized in that it hasa pitch of 14 mm.